Oxidation process for the synthesis of {60 -hydroxy esters

ABSTRACT

A process for the synthesis of Alpha -hydroxy esters of carboxylic acids by reacting a carboxylic acid ester with a hydroperoxide in the presence of a metal ion catalyst. The reaction is characterized by mild reaction conditions and good efficiency. The Alpha -hydroxy esters are useful intermediates in the production of acrylates.

United States Patent Trecker et al. 51 July 18, 1972 [54] OXIDATIONPROCESS FOR THE [56] References Cited SYNTHESIS OF a-HYDROXY ESTERSUNITED STATES PATENTS [72] Inventors: David J. Trecker, SouthCharleston, W.

Va; J E. Mcxeonnmmwood, NY. 2,782,219 2/ 1957 Cleaver ..260/484 X [73]Assignee: Union Carbide Corporation, New York, 'f weinbel'gel' AssistantExaminer-Paul J. Kilios Attorney-Paul A. Rose and Louis C. Smith, Jr.[22] Filed: Aug. 12, 1969 211 App]. No.: 849,515 [57] ABSTRACT A processfor the synthesis of a-hydroxy esters of carboxylic acids by reacting acarboxylic acid ester with a hydroperoxide [52] US. Cl. ..260/484 R,260/4109, 260/468 R, in the presence ofa metal ion catalyst. Thereaction is charac 260/468 260/473 260/479 260/483 terized by mildreaction conditions and good efficiency. The 260/485 260/486 D a-hydroxyesters are useful intermediates in the production of s 1 int. Cl... 60%69/66 acrylates. [58] Field of Search .,260/484, 468, 473, 610 R 8Claims, No Drawings OXIDATION PROCESS FOR THE SYNTHESIS OF a- HYDROXYEI'ERS This invention relates to the production of a-hydroxy esters.

The formation of both a-hydroxy esters and a-hydroxy acids in goodyields on a large scale is particularly desirable, for these compoundsserve as intermediates in the formation of acrylates. The a-hydroxyesters or acids can be subsequently dehydrated to give the correspondingacrylate or acrylic acid.

Methods for making these useful intermediates have taken a variety offorms. For instance, a-hydroxy isobutyric acid has been prepared byreacting t-butyl alcohol or isobutylene with an excess of fuming nitricacid or dinitrogen tetroxide. However, the special handling required ofthe corrosive materials involved and the vigorous reaction conditionsare deterrents to the use of this reaction.

Methacrylic acid has been produced by the oxidation of methacroleinmanufactured by the air-oxidation of isobutylene while employingheterogenous catalysis. This reaction is noted for its randomnes andalso for its predisposition to form unwanted intermediate products whichlend thenselves to still further desirable side reactions.

Methyl a-hydroxy isobutyrate, which upon dehydration forms methylmethacrylate, has been produced by the air-oxidation of methylisobutyrate. A disadvantage of the reaction is its low yields, which arecaused by the randomness of the reaction.

It is an object of this invention to produce acrylate intermediates inhigh yields.

It is another object of this invention to produce acrylate intermediatesusing mild reaction conditions.

It is yet another object of this invention to produce acrylateintermediates in high yields while using mild reaction conditions.

These and other objects will become obvious by the following descriptionof the invention.

It has now been found that a-hydroxy esters can be produced bycontacting an ester of a carboxylic acid with a hydroperoxide in thepresence of a metal ion catalyst while in the liquid phase. This novelprocess involves mild oxidation conditions, but nevertheless renders ahigh selectivity. More particularly, the oxidation process concernscontacting an ester of a carboxylic acid with a hydroperoxide in thepresence of a metal ion catalyst selected from the Group 48, 5B, 6B, 7B,8 and 1B metals, with Group 7A and 8 metals preferred. It is imperativethat the carboxylic acid ester utilized have at least one hydrogen atomon the carbon adjacent to the carbonyl of the ester function in order toallow oxidation to take lace. p A preferred embodiment of the reaction,the formation of methyl a-hydroxy isobutyrate from methyl isobutyrate,is

graphically shown below:

CH I

il Metal ion The process is applicable to any aliphatic ester of acarbox- I ylic acid which contains at least one hydrogen atom on thecarbon adjacent to the ester carbonyl group. Various examples of thescope of the invention, setting forth the ester and the resultinga-hydroxy ester are tabulated below.

Z-endoCarbomethoxynorbornane 2-exo-Hydroxy-2-endo- Hydroperoxides whichmay be used in the process of this invention include ethylhydroperoxide, n-propyl hydroperoxide, t-butyl hydroperoxide, bamylhydroperoxide, cumene hydroperoxide, benzyl hydroperoxide, ltetralinhydroperoxide, p-tolyl hydro-peroxide, and the like. The tertiaryhydroperoxides such as t-butyl hydroperoxide, t-amyl hydroperoxide, andcumene hydroperoxide are particularly effective.

Various metal ion catalysts from Groups 48, 5B, 6B, 7B, 8 and 18 shownto be useful in the invention include dicyclopentadienyl titaniumdichloride, vanadyl acetylacetonate, vanadic trioctanoate, chromiumtriacetate, chromoyl caproate, manganic stearate, ferrous stannate,ferric acetylacetonate, cobalt octanoate, cobalt naphthenate, cuprousacetate, cupric acetate, manganic acetylacetonate, vanadiumoxyacetylacetonate, nickel(1l) acetylacetonate, cerium(Il) acetate, andthe like. The manganese and cobalt salts are especially preferred.

it has been found that the best working combination is the coupling oft-butyl hydroperoxide as the oxidant with cobalt naphthenate as thecatalyst.

Thereaction is carried out generally by mixing in the liquid phase thealiphatic ester of the carboxylic acid, the hydroperoxide, and the metalion catalyst. There. are four alternatives for the mixing process; theingredients can be mixed together simultaneously, the catalyst can beadded incrementally to a solution of the ester and peroxide, thehydroperoxide can be added incrementally to a solution of the ester andcatalyst, or the catalyst and ester can be added portionwise to thehydroperoxide. The preferred method is to add the catalyst in incrementsto a solution of ester and hydroperoxide. The mole ratio ofhydroperoxide: ester can range from 5 to 0.01, with a preferred range of2 to 0.05 and a most preferred range of l to 0.1. The ratio of catalyst:hydroperoxide can range from 1 to 0.00001; preferred is a range between0.1 and 0.0001 and most preferred is a range of 0.01 to 0.001.

The reaction must be can'ied out in the liquid phase and, although asolvent is not required, an inert reaction medium can be employed. Thebest solvents are those which do not coordinate with the metal catalystsor react with the hydroperoxides. It is convenient to use the alcoholcorresponding to the hydroperoxide employed; for example, I- butylalcohol is used when t-butyl hydroperoxide is used as the oxidant.

The reaction can be carried out at any temperature between 30 and 120C., bearing in mind that the reaction solution is to remain liquid atall times. The preferred temperature range is 0 to C. and the mostpreferred range is 20 to 60 C. lt is very convenient in practice tocarry out the reaction at ambient conditions.

The reaction may be carried out in air, in an enriched oxygenatmosphere, or in an inert atmosphere such as nitrogen, argon or helium.There appears to be no advantage in conducting the reaction in any sortof artificial atmosphere. The resulting a-hydroxy ester is isolated byusing fractional distillation.

After the a-hydroxy ester has been isolated, it can easily be convertedto the corresponding acrylate by dehydration, such as methyla-hydroxyisobutyrate changed to methyl methacrylate as described in US.Pat. No. 2,303,842; Ger. Pat. No. 1,795,295; Ger. Pat. No. 1,191,367;and Fr. Pat. No. 1,215,702. Any of these several known procedures can beused. The acrylate then can be vinyl polymerized to the polyacrylatesuch as poly( methyl methacrylate). Poly(methyl methacrylate) iscurrently produced on a multimillion pound a year basis for use incastings and moldinp which call for high clarity, strength and lightweight. It is used in Windshields, safety shields, and variousautomobile parts. The acrylics, in general, are also used as adhesivesand in coatings. Acrylic emulsions are used as leather and textilefinishes and the clear coatings are used as polished metal finishes.Enamels based upon the acrylics are useful for heat and fume resistanceapplications.

For the working examples, the oxidation involved a simple liquid phasetreatment of methyl isobutyrate with t-butyl hydroperoxide and variousmetal ions. Nine metal species were scanned with the results summarizedin Table I. Dimethyl tetramethyl succinate, a radical coupling product,was always formed as a minor coproduct as shown in the followingreaction.

- Cat. (CH-,OgCHCOsCI-I: t-BuOOH methyl a-hydroxyisobutyrate. Theseresults, compiled in Table IV, indicated that at ester conversions of ca6 percent, methyl a-hydroxyisobutyrate could be obtained in efiicienciesof 84-88 percent, based on ester, and 44-46 percent, based onhydroperoxide.

The treatment of methyl isobutyrate with t-butyl hydroperoxide alone atroom temperature, as well as the treatment of methyl isobutyrate with ametal ion catalyst alone, gave no reaction whatsoever. However, theuncatalyzed reaction of t-butyl hydroperoxide with methyl isobutyrate atelevated temperatures 120 C) resulted in the formation of methyla-hydroxyisobutyrate and dimethyl tetramethyl succinate, usually incomparable amounts. Similarly, the ultraviolet radiation of methylisobutyrate and t-butyl hydroperoxide gave rise to moderately goodyields of methyl a-hydroxyisobutyrate and dimethyl tetramethylsuccinate. These runs are summarized in Table V. It will be noted that,in all these instances, the selectivity of methyl a-hydroxyisobutyratewhich was obtained with metal ion catalysts was lacking.

The methyl a-hydroxyisobutyrate was isolated and identified bycollection at 69 C. (30 mm) using fractional distillation. The infraredspectrum showed OH stretching (3,250 cm") and an ester carbonylabsorption (1,728 cm"). The N.M.R. spectrum of methyla-hydroxyisobutyrate confirmed its assigned structure.

Although the working examples show only the conversion of methylisobutyrate to methyl a-hydroxyisobutyrate, the process is applicablefor the conversion of any carboxylic acid ester having at least onehydrogen atom on the carbon adjacent to the carbonyl of the esterfunction.

TABLE I.EFFECT 0F VARYING METAL CATALYST Methyl a- Dimethyl Reactionhydroxyisotetramethyl time, butyratc, succinate, Example .\letalcata1ystMole ratio Conditions hours percent percent Co naphthenatc... 5:1:0. 002Room temperature 1 13.4 1.: V (Acac): 51110.00 d0. 2 4.4 1..1 Fe(Acac)3... 5:1:0. 2 5.5 2.11 Grill (0A0): -5:1:0. '1 5.5 1.0 Mn" (Acac):521:0. 2 12.0 Trace N1 (Aeac)2------" 521:0. .2 Trace 1.1 Ti" (C511C11..." 5:1:0. .2 Trace Trace Cu OAc 5:120. .3 2.1 Trace Ce(OAe)a........ 7.8zlz0. 2 5.4 Trace B Methyl isobutyratezt-Bu0 OH:metal. b Yield, based on starting t-BuOOH.

TABLE 1I.-EFFEC'1 OF TEMPERATURE 'lemltc- Methyl a- Dimethylpt'i'naction hydroxytetramethyl lure. time, isobutyrate sut-t'innteExample Metal catalyst \lolerntiu hours percent percent Conaphthenate... 7.8:l:0.003 (i 14; 'Iract- C0 naphthenate... 5:1:0.U02 2516 15.6 Co naphthenate... 5:1:U.002 115 16 10.0 1.1 Mn (Acaeh...7.8:l:0.00.1 ti 84 6.3 Mn (Acae)3 521:1).006 25 16 13,11 Mn (Acacn.5:l:0.006 .15 1H 11.3 'lrace Fe (Acuch. 521:0.006 25 2 5.5 2.0 Fe(Acac)s. 5:110. 006 16 6.11 1.7 Cr (0AC)3.. 5:1:0.0l2 25 2 5.5 1,0 Cr(0Ac)a 5:1:0.012 .15 16 10.4 1.5 N1." (A0862. 5:1:0.008 25 2 Trace 1.1Ni (Acac) 52120.008 .15 16 Tran- 1.3 'Il (0511511017. 521:0.008 25 2Trace 6b Ti (C5H5):Cl,. 5:l:0.008 .15 1G Trace 1 Methylisobutyratezt-BuOOHzmetal. 1 Yield, based on starting t-BuOOII. 3 Notdetermined.

TABLE I11 [Ellect of catalyst concentration and hydroperoxideconcentration} Methyl a- Temper- Reaction hydroxyiso- Dimethyl ature,time, hutyrate tetramethyl Example Metal catalyst Mole ratio C. hrs.percent succinate 1 Co naphthenate. 5:l:0.002 '25 15 20.4 1.59,v 2Co"naphthenate- 5: 1:0. 010 25 72 17.3 3... Co naphthcnatc 52210.002 '2516 23.3

I Methyl isobutyratezt-BuOOHzmetal. Yield, based on starting t-BuOOH.

= Not determined.

TABLE IV [Effect of incremental addition of hydroperoxide and of metalcatalyst] Yield of Efficiency to methyl methyl aa-hydroxyisobutyrato,

hydroxypercent isobutyrate, Example Metal catalyst Mole ratio aConditions percent (h) (o) 1 co naphthenate.. 7. 7:1:0. 005 Co was addedgradually over a period of 72 hrs 4 39. 37 7 43, 7 "2.. \ln (Acac)a. 7.l: Mn was added gradually over a period of 72 hrs 35.1 83.7 46. 1 71-0Ce was added gradually over a period of 72 hrs... 6. 6 (Lu was addedgradually over a period of 72 hrs 5. 8

e Methyl isobutyrate:t-Bu0OHzmetal. b Based on methyl isohutyrate.

0 Based on t-BuOOH.

Determined after 72 hrs. s Unreliable conditions, due to low conversionto methyl a-hydroxyisobutyrate.

TABLE [Uncatalyzed runsnefiect of heat and ultraviolet light] Reac-Methyl a- Dlmethyl tion hydroxyisotetramethyl Mole Conditions, time,butyrate, suceinate, Example ratio A 0. hours percent percent 12 20. 632. 3 12 13. 6 27. 1 40 2. 6 3. 6 40 3. 9 6. 5 120 40 9. 0 8.9 U.V.light, 25- 72 38. 1 31. 0

Methyl isobutyratezt-BuOOH. Yield, based on starting t-BuOOl-I. c100watt medium-pressure mercury arc; Vycor optics.

What is claimed is:

l. A method for synthesizing a-hydroxy esters from aliphatic or phenylesters of carboxylic acids having at least one hydrogen atom on thecarbon adjacent to the carbonyl function of the ester which comprisesreacting said carboxylic acid ester in the liquid phase with ahydroperoxide, in the presence of a metal ion catalyst selected from thegroup consisting of Group 4B, 5B, 6B, 7B, 8, and 1B metals.

2. The method according to claim 1 wherein said hydroperoxide is atertiary hydroperoxide.

3. The method according to claim 1 wherein said metal ion catalyst isselected from the group consisting of the Group 78 and 8 metals.

4. The method according to claim 1 wherein said metal ion catalyst isselected from the group consisting of cobalt and manganese catalysm.

5. The method according to claim 1 wherein said carboxylic acid ester ismethyl isobutyrate.

6. The method according to claim 5 wherein said hydroperoxide is t-butylhydroperoxide, and said metal ion catalyst is cobaltfll) naphthenate.

7. A method for synthesizing a-hydroxy esters from aliphatic or phenylesters of carboxylic acids having at least one active hydrogen atom onthe carbon adjacent to the carbonyl function of the ester whichcomprises reacting said caragid ester in the liquid phase with ahydroperoxide in the presence of a metal ion catalyst selected from thegroup consisting of Group 48, 5B, 6B, 7B, 8 and 1B metals wherein saidcatalyst is added incrementally to a solution of said hydroperoxide andsaid carboxylic acid ester.

8. A method for synthesizing a-hydroxy esters from aliphatic or phenylesters of carboxylic acids having at least one active hydrogen atom onthe carbon adjacent to the carbonyl function of the ester whichcomprises reacting said carboxylic acid ester in the liquid phase with ahydroperoxide in the presence of a metal ion catalyst selected from thegroup consisting of Group 48, 5B, 6B, 7B, 8 and 1B metals, said reactionbeing carried out under ambient conditions.

l i I I

2. The method according to claim 1 wherein said hydroperoxide is atertiary hydroperoxide.
 3. The method according to claim 1 wherein saidmetal ion catalyst is selected from the group consisting of the Group 7Band 8 metals.
 4. The method according to claim 1 wherein said metal ioncatalyst is selected from the group consisting of cobalt and manganesecatalysts.
 5. The method according to claim 1 wherein said carboxylicacid ester is methyl isobutyrate.
 6. The method according to claim 5wherein said hydroperoxide is t-butyl hydroperoxide, and said metal ioncatalyst is cobalt(II) naphthenate.
 7. A method for synthesizing Alpha-hydroxy esters from aliphatic or phenyl esters of carboxylic acidshaving at least one active hydrogen atom on the carbon adjacent to thecarbonyl function of the ester which comprises reacting said carboxylicacid ester in the liquid phase with a hydroperoxide in the presence of ametal ion catalyst selected from the group consisting of Group 4B, 5B,6B, 7B, 8 and 1B metals wherein said catalyst is added incrementally toa solution of said hydroperoxide and said carboxylic acid ester.
 8. Amethod for synthesizing Alpha -hydroxy esters from aliphatic or phenylesters of carboxylic acids having at least one active hydrogen atom onthe carbon adjacent to the carbonyl function of the ester whichcomprises reacting said carboxylic acid ester in the liquid phase with ahydroperoxide in the presence of a metal ion catalyst selected from thegroup consisting of Group 4B, 5B, 6B, 7B, 8 and 1B metals, said reactionbeing carried out under ambient conditions.